This invention relates to a device for tracing surfaces, particularly closed surfaces each of which may be used as a reference for the edging of an eyeglass lens to cause it to fit into a given lens opening in an eyeglass frame, to provide output data describing the shape of the traced surface; and deals more particularly with improvements in such a device permitting the tracing operation to proceed substantially automatically, quickly and accurately with very little pressure having to be applied to the traced member.
The device of this invention has been developed and is particularly well adapted to the tracing of a surface defining a shape to be applied to an eyeglass lens during its edging to cause it to fit properly into the lens opening of a given eyeglass frame. Accordingly, the invention is described and illustrated herein in association with such an application. It is to be understood, however, that in at least its broader aspects the invention may be applied to other applications where it is desirable to obtain data describing the shape of surfaces, especially closed or substantially closed ones. Therefore, it is intended that the scope of the invention not be limited only to tracing devices applied to the field of eyeglass manufacture.
In the eyeglass field, an apparatus for performing substantially the same function as the apparatus of this invention is already known from U.S. Pat. No. 4,724,617. That is, the apparatus of said patent is one for providing data describing the shape of a lens opening of a given eyeglass frame by moving a stylus along the closed surface of the frame defining the opening, detecting the position of the stylus at many points during its traverse along the closed surface with reference to a given coordinate system, and then processing the detected points to provide a set of output data describing the shape of the traced surface and usable subsequently by an edging machine to edge an eyeglass lens to a shape matching that of the lens opening. The stylus, however, is guided manually along the surface to be traced. This makes the tracing operation relatively slow and subject to human errors. It is difficult for an operator to apply a small steady force to the stylus during the tracing process with the result that often, especially in the case of a light flimsy frame, the frame may be bent seriously out of shape during the tracing procedure causing the apparatus to output inaccurate shape data. The problem of frame bending during tracing can be attacked by holding the frame at a large number of points along the circumference of the lens opening to better counteract the bending forces applied by the stylus, but this substantially increases the cost and complexity of the holder and greatly increases the time required to move a frame into and out of the holder.
The general object of this invention is therefore to provide a surface tracing apparatus avoiding the problems mentioned above. Particularly, the object is to provide an apparatus wherein the tracer stylus or other tracer element is moved automatically along the surface to be traced, without human guidance, in a rapid and precise way to allow the tracing operation to be performed in a short time, and whereby the tracer element exerts only a very low force on the traced surface to inhibit distortion of the surface shape.
A further object of the invention is to provide an apparatus of the foregoing character particularly adapted to the tracing of a closed surface defining the lens opening of an eyeglass frame whereby such low forces are exerted on the frame by the tracer element that even relatively flimsy frames can be accurately traced using a relatively simple and quickly operated holder for the frame. That is, a simple holder holding a frame only in the vicinity of the nose piece area can be used for practically all frames without additional holding points having to be provided for weak frames.
Another object of the invention is to provide a tracing apparatus of the foregoing character which may be used either for the tracing of the lens opening of an eyeglass frame, where the traced surface faces inwardly toward the rotational axis of the tracer element, or to trace a lens pattern, a dummy lens or an actual lens where the closed surface being traced faces outwardly away from the rotational axis of the tracer element.
Other objects and advantages of the invention will be apparent from the following description of the preferred embodiments of the invention.